This invention concerns the opening of tobacco cases after preconditioning, in particular bales of Oriental or Turkish or small leaf tobacco.
It is customary to store tobacco leaf in a dried condition at around 12% moisture content and compressed into packages in the form of wooden hogsheads, cardboard cases or hessian covered bales.
When these packages arrive at the factory for processing into cigarettes or other tobacco products they have to be opened, in the sense of separating the leaves, without breakage.
At 12% moisture content the leaf is fragile and easily broken, so the opening of the package is preceded by a conditioning process which heats and adds moisture to render the leaf supple. This is known as pre-conditioning.
The pre-conditioning process has to be effective while the leaves are still in the compressed package form, so it is normally carried out by a vacuum process, in which the air is evacuated from the package and replaced by steam which heats the tobacco and adds moisture by condensation, throughout the package.
Having pre-conditioned the leaves in the package it is then subjected to an opening process to separate the leaves and feed them to a further conditioning stage. This can be by hand, but is normally by a pin feed device known in the art as an "auto feed".
The auto feed comprises an elevating band conveyor set at approximately 55 degrees to the horizontal in the open, with an arrangement of pins on its surface. At the low end of the elevating band there is a hopper arrangement with a plain horizontal band conveyor.
The preconditioned package of tobacco is dumped into the hopper and conveyed toward the elevating band. The pins lift tobacco from the bulk in a layer. A doffer consisting of tines on a rotating shaft levels this layer to the depth of the pins, by throwing surplus leaf back into the hopper.
In practice this process does not totally separate the leaves and there are bunches or "pads" of leaves still sticking together in the product leaving the auto feed.
Because the preconditioning process adds moisture by condensation and heating the tobacco, the addition is limited to around 1% per 15 degrees C rise by the specific heat of the tobacco. This moisture can readily be lost by evaporation as the tobacco cools, so is only temporary moisture.
For the subsequent processing of the leaf, for example threshing or cutting, the leaf must be moistened to around 20% moisture content. The tobacco is therefore subjected to a further conditioning process in a rotating cylinder through which hot saturated air is circulated.
This conditioning cylinder is fitted with internal paddles or pins which lift and tumble the tobacco and reheat it again by condensation. The heat renders the tobacco receptive to the addition of permanent moisture by sprays which are directed into the cylinder.
The action of the cylinder further opens the leaf "pads", but some still remain in the discharge from the cylinder. These are undesirable for subsequent processing as the leaf within the "pads" does not experience the further conditioning and is thus still dry and would be degraded by the subsequent processing.
There is a particular problem with Oriental leaves where small bunches of leaves are threaded together for the curing stage. These tend to stick together in "pads" more persistently than leaves which are pressed together into a bale after curing.
It is usual to pass the discharge from the conditioning cylinder into a vertical air leg or classifier to separate the "pads" from the individual leaves; the "pads" being recirculated back to the auto feed for further treatment within the auto feed and cylinder.